Blake returned from Berlin in April 1959. His wife, Gillian, was pregnant and Blake took up a temporary London posting. Throughout this home posting he continued to pass high-level intelligence to his contact at the Soviet Embassy.

In September 1960, he was sent to MECAS to study Arabic. The Middle East was becoming increasingly important for Britain and the West and MI6 needed men of Blake’s calibre out there, speaking the language. The standard length of the MECAS Arabic course was eighteen months, so Gillian and their two sons accompanied Blake. He fell quickly into stride, having had a fair grounding in the language as a boy with his uncle and cousin in Cairo.

In April 1959 – just as Blake was leaving Berlin – the CIA started to receive secret information from an unidentified informant in the Polish Military Intelligence (the UB). There were two particular items of intelligence that required further investigation: someone in the British Royal Navy was spying for the Soviet Union; the informant had seen secret documents originating from a Soviet agent inside MI6. Details were limited, and the identity of those involved unknown.

Towards the end of 1960, the KGB learned that the United States had a double agent in the UB. They attempted to warn the UB, but by good fortune the person who received this KGB message was the double agent himself. His name was Colonel Michael Goleniewski and he was the head of the UB station in East Berlin.

Goleniewski was able to escape before anyone else saw the message. He fled to West Berlin, contacted the CIA, and was then flown to Washington for debriefing. The information he gave was now much more detailed. He told the Americans that the Royal Navy informant was passing technical secrets about the Navy’s latest underwater weaponry being developed and tested at the Admiralty Underwater Weapons Establishment at Portland. Goleniewski believed this spy had been recruited several years earlier and may actually have served in Poland, presumably in the British Embassy.

With regard to the Soviet agent inside MI6, Goleniewski said he had received copies of documents originating from that source. These often contained the names of MI6 field agents and targets.

The CIA informed MI6 and offered to send Goleniewski to London for further debriefing, which resulted in the positive identification of Harry Houghton as the Royal Navy spy. He had been a clerk in the Naval Attaché’s Office in the British Embassy in Warsaw from 1951 to 1953.

Houghton was arrested on 7 January 1961, together with four other members of the Portland spy ring: Konon Molody (alias Gordon Lonsdale), Ethel Gee, Peter Kroger and Helen Kroger. The Krogers were later identified as Morris and Lona Cohen.

Houghton and Gee were each sentenced to fifteen years in prison, the Krogers (Cohens) to twenty years each and Lonsdale (Molody) to twenty-five.

Some of the officers involved in the investigation and arrests became suspicious that Lonsdale, and possibly also the Krogers, had been warned in advance that they were under intense official scrutiny. Evidence from cross-examinations at the trial lent some support to these suspicions.

MECAS – the Middle East Centre for Arabic Studies – was a language centre in the Christian village of Shemlan in the Lebanon. It was opened by the British government in 1947 and soon became famous throughout the world as possibly the best place to learn Arabic. Lord Hurd of Westwell (former British Foreign Secretary) wrote: ‘To the Israelis MECAS was the place where Britain trained its brilliant young men to be sentimental about the Arabs and hostile to Zionism. To many Arabs it was simply the “School for Spies”, the heart of Britain’s post-war strategy of dominating the Middle East through its intelligence agencies.’ MECAS was closed in 1978 due to civil war in the Lebanon.

Lonsdale (Molody) was exchanged for Greville Wynne in 1964.